Calcium catalysis in air gasification of cellulosic chars

Cellulosic chars containing calcium have been prepared from carboxymethyl cellulose in the calcium form and from pure cellulose containing sorbed calcium acetate, at several heat treatment temperatures (HTTs) in the range 400–900°C. The chars have been gasified in air at 300°C. The results indicated a general decrease in reactivity with increasing HTT. However, instead of a monotonic decrease in reactivity reported previously for coal chars containing indigenous or added calcium, the reactivity versus HTT curve consisted of three distinct regions which probably reflect the transformations being undergone by the catalyst species on increasing the HTT. Crystalline CaO was detected by XRD only in chars heated to 1000°C, at which temperature the catalyst was no longer effective. The relationships between gasification rate and catalyst concentration and also mode of addition have been determined using chars of HTT 600°C. As found by earlier workers with some coal chars, the rate reached a maximum with increasing calcium content and then declined. Chars containing sorbed calcium showed a relatively early decline of rate. They also showed less reactivity than the chars containing ion-exchanged calcium at all calcium concentrations.